RF memory circuits, or loops, are currently in use for non-coherent signal interception and retransmission. RF memory circuits are used to store desired RF signals, such as signals from hostile radars or communications, for various electronic warfare (EW) and electronic intelligence (ELINT) applications. Such applications include coherent radar jamming, spoofing and deception, as well as coherent communication jamming and deception. Generally, these applications are achieved through processing circuits which alter the signal received from a hostile source and retransmit the altered signal so as to convey false information.
Typically, the hostile signals are deliberately made difficult to detect. They may be transmitted at very low power, or in bursts of very short duration. Very often, such signals contain embedded codes, which a hostile radar, for example, checks for in the return in order to distinguish a true return from a false signal. In addition, because radar and communications signals are typically of very high frequency, the duration of such signals is very short. The RF signals to be captured, processed and retransmitted thus may exist only for fleeting instants and may cease to exist before the EW and ELINT circuits are capable of processing them. It is therefore necessary to have a memory circuit capable of storing the RF signals so that they can be available to the EW and ELINT processing circuits.
Digital RF memory circuits (DRFMs) have been used in the past for coherent RF signal capture, storage and retransmission. Coherent capture is vital if a false signal is to have the same spectral characteristics as the incoming signal. If the signals are captured non-coherently, spoofing or decoding may be ineffective or impossible. DRFM circuits have some drawbacks, however. The DRFM's instantaneous bandwidth is presently limited typically to less than one GHz, which is inadequate in most cases. In addition, the DRFM's digitalization process inherently contaminates the incoming RF signals with spurious noise, which distorts the RF signal. DRFMs also operate poorly in a simultaneous signal environment, which is usually the situation in most realistic applications.
Analog RF memory loops have also been used, but have been limited to non-coherent signal intercept and retransmission. Although analog RF memory loops avoid the drawbacks of DRFMs, analog memory loops have heretofore been impractical for coherent intercept and retransmission.
The present invention makes it possible to employ analog RF memory loops with coherent signal processing, eliminating the need for DRFMs and their drawbacks. Thus, the present invention makes it possible to achieve the advantages of analog RF memory loops in coherent intercept and retransmission applications.